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Four gametes are made during cell division by meiosis. The gamete cells have half the number of chromosomes as the cell.
Click on image for full size Courtesy of National Center for Biotechnology Information, NIH

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Meiosis: How Gametes Are Made

Plants, animals and many other species within the domain Eukaryota are able to make offspring, or young, by sexual reproduction. Their offspring are made from gametes.

Gametes are special cells that have only half the number of chromosomes. When two gametes fuse together, they make one cell that has the correct number of chromosomes, with half of those (one from each pair) coming from the mother and the other half coming from the father. This set of chromosomes becomes the genetic instructions that describe how the individual will grow and develop. Usually only gametes from the same species are able to fuse together to make offspring.

Forming the gametes requires cells to undergo a special type of cell division called meiosis, which is really two cell divisions happening one after the other. Meiosis will only happen to cells in the male or female sex organs of a plant or animal. The result is that one cell becomes four gametes that each has a single set of chromosomes, half the total number in the original cell.

Gametes only contain one copy of each gene, but the cell they were made from contained two varieties of each gene. The genes in each gamete are chosen randomly from each pair during meiosis. One variety or the other will be passed on to the offspring.

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